Plastic die steel wide range of applications, strict performance requirements, to avoid deformation and good corrosion resistance; Free-cutting plastic mold steel heat treatment.
Plastic die steel, as a kind of die steel used in plastic production, mainly consists of die steel. Generally, it can be divided into age hardening plastic die steel (including mirror die steel), corrosion resistant plastic die steel, carburized plastic die steel, prehardened burying die steel (including free cutting steel), quenched and tempered plastic die steel and hardened die steel. Plastic mold steel six major categories. Age-hardening plastic die steel, carburized plastic mold steel and pre-hardened plastic mold steel are widely used.
The main characteristics of plastic die steel: plastic die steel is widely used, from ordinary steel to special steel, special steel has its own system, steel number before adding SM; performance requirements are strict, heat treatment is difficult, can be polished and mirror surface quality Og, avoid deformation; Good corrosion resistance; free cutting.
All kinds of steel forms of plastic die steel are heat-treated by metal mould heat treatment furnace:
1. Heat treatment of pre-hardened plastic die steel. The typical pre-hardened plastic die steel is SM3Cr2Mo whose heat treatment process is 8 40-880 °C floating fire, oil cooling, 600-650 °C tempering, air cooling and supplying hardness 32HRC. The corresponding U. S. steel is P20, German steel 40CrMnMo7, Japan HPM2. The heat treatment process of P20 steel after Carburizing is 820-870 °C, 150-260 °C tempering and air-cooling. The hardness of Carburizing layer is 58- 64HRC. The permeability of German steel 40CrMnMo7 is better than that of SM3Cr2Mo, and the workability and polishing are better.
2. One or more free cutting alloying elements should be added to the free cutting prehardened steel on the premise of ensuring the original properties. The typical materials are: 8CrMnWMoVS (8CrS), free cutting steel containing S, the machinability of T10A steel (200HBS) is comparable to that of annealed T10A steel when the hardness of hot place is up to 40 ~ 42 H RC, and its polishing ability and lithographic etching property are better than that of annealed T10A steel. Typical heat treatment: annealing at 800 ±10 °C for 2 ~ 4 h, cooling to 700 ~ 720 °C for 4 ~ 6 h, furnace cooling, hardness <=229HSB,880-920 °C, air cooling, hardness 63HRC, tempering at 160 ~ 200 °C, air cooling, hardness ≥ 58HRC.
(3) High toughness free-cutting steel: 5CrNiMnMoVSCa.
4. The non-alloyed medium carbon plastic die steel is a kind of medium carbon structural steel with higher metallurgical quality (purity). The carbon content is in the range of 0.4% to 0.6%. Typical materials are: SM45, SM5 0, the same Japanese steel is S45C-S58C. Its heat treatment process is no different from the conventional process, for small, not high precision plastic mold parts.
5. C-infiltrated plastic die steel: for the parts of plastic mould with large impact, the tough surface and hard center are required, and the C-infiltrated steel is adopted. General parts using 20Cr. Special steel is used for parts with high surface quality: 12CrNi3A.
6. Corrosion-resistant plastic die steel is used for manufacturing plastic products and die parts which have corrosive effect on metals. The typical steel grades are: Cr13, 9Cr18 and so on may strengthen the martensite stainless steel. Its heat treatment and general stainless steel products heat treatment is the same. Age-hardening plastic die steel: Age-hardening steel is used to reduce heat treatment deformation and improve precision retention of plastic mold parts with complex shape, high precision and long life. The mould parts become soft after solution treatment (28-34HRC), which is convenient for forming and then age-hardening, so as to obtain the required comprehensive mechanical properties.
7. Maraging hardening steel has high ratio of yield to strength, good machinability and weldability. The typical steels have hardness of 28HRC in solution state and aging of 480C for 3h, the hardness can be increased to 43HRC, the holding time is longer, and the hardness is up to 52HRC. The precipitation hardening steel is strengthened by solution treatment and precipitation of the second phase, and the hardness can reach 37-43HRC. The representative steel number is 25CrNi3MoA1.